when it comes to gas how low is too low on octane?

[LW_Icarus]

yet another fuel observation-turbo blue or cam2 will sink neoprene floats.and sometimes harm coatings in the carb. Ive put cam2 in a perfectly good motorcycle and had a gas leaking mess overnight. fuel additives will sometimes do the same, although I believe the formulas are better now.

but after some modifications and retuning my old bikes loved race gas. back then I was feeling ripped off paying 2.30 a gallon for the stuff lol.

back to the original posters observation of a hot running bike, and blue pipes, if it really is ultra hot(which could be verified with a raytek temp gun) then you are leaning out. 14.7:1 I believe is the ideal mixture to combust gas/air, anything leaner (more air) will run exponentially hotter.

look at your intake boots. probably the most likely cause of a vacuum leak. a little gumout sprayed around em with the engine running will quickly identify leaks.

[gsBert]

oh gawd, dont tell me were talking about octane again.

i'll talk about the gas first, then about your running hot problem (the two are not related in any way)

first of all speedie, because your buddy's been riding 30 years doesnt mean he knows squat about engines, chemistry, or motorcycles. (heck my dad's been riding a long time and when i told him about counter-steering he called me a liar)

if you're running hot, it had nothing to do with octane. it has to do with mixture. (air/fuel ratio, just like when you use an oxyacetylene torch, more oxygen, more heat, less oxy, less heat)

about octane:
you should use the lowest octane rating gas possible, that is use 87 unless your engine pings, and if it pings, make sure its not because off timing or other stuff.
if you've been running super all along you might have carbon deposits in your combustion chambers that could cause hot spots and make it ping on regular gas unless you clean your combustion chambers.

here's how to clean the engine out without taking it apart:
- warm up your engine
- remove the air filters or air box and idle the engine fastish 2500 rpms
- use a spray bottle to spray fine water mist into your carb intakes
- you'll likely get lots of smoke and a bit of hesitation, dont worry, no harm will come of it

here's what it does:
the super youve been running doesnt all combust because it's well, too high octane for your engine (hight octane=less combustible)
the unburnt gas caused carbon deposits as i've said.
when the water mist hits your combustion chamber walls it flashes to a boil and detaches those deposits (they'll spit out your exhaust)

run about 1/8 cup through each cylinder that way and your engine should be cleanish. you can now run on regular.

about running hot now:
the pipes turn blue, its a fact of life. the way of telling if your engine is running too hot is to remove the plugs and stick your finger in, just kidding.
plugs should be a nice tan color, if they are white, you're running too hot, which means your carbs are too lean. if they're black you're running too rich which means your carbs are too rich and you shouldnt be getting your engine too hot unless you have an oiling problem (your bike is oil-cooled) or a very dirty engine (your bike is air-cooled also). also different plugs have differnet heat ranges. make sure your plugs are what came stock on your bike (ask a bike shop for the proper heat range) and gapped properly.

different people will have different opinions, but if you wanted information, you just got it.
do things in this order:
- give your engine a good wash (make sure the cooling fins are clear of dirt)
- make sure there are no intake vacuum leaks anywhere (listen with a hose)
- decarbonize your engine as described above
- check the timing
- check the sparkplugs
- get an oil change (how many miles you got?, i like using 20-w50)
- rejet your carbs if necessary to compensate for the potentially lean condition

[duaneage]

Octane is the ability of the gasoline to resist detonation. Period.
The combustion takes place in .003 of a second regardless of octane. High octane gas does not burn faster or slower than low octane gas. It does not carbon a head, dirty airfilters, weak spark, oil burning and poor jetting cause carbon buildup, not super unleaded.

While true that too high an octane is a wste of money, at 80 cents a tank more I prefer Super unleaded because the bike will not ping, ever, under load in the summertime.

[Anonymous]

Octane is the ability of the gasoline to resist detonation. Period.

That's the way I understand it as well. Detonation = pre-ignition. Unless I'm mistaken, higher compression tends to encourage pre-ignition, and higher octane allows the fuel to resist this in order to fire at the right time.

Perhaps the faster/slower idea is a slightly mis-stated version of sooner/later.

Willing to stand corrected,
Steve

p.s. I've been *@%^$*@%^$*@%^$*@%^$ing for over 30 years, but that doesn't mean I know how kidneys work.

[duaneage]

[quote="SteveO"]

Octane is the ability of the gasoline to resist detonation. Period.

That's the way I understand it as well. Detonation = pre-ignition. Unless I'm mistaken, higher compression tends to encourage pre-ignition, and higher octane allows the fuel to resist this in order to fire at the right time.

Perhaps the faster/slower idea is a slightly mis-stated version of sooner/later.

Correct a mundo

Flame travel speed is the same regardless of octane, no harm is done with extra quality. pre-ignition cannot always be heard by the rider but the connecting rods and bearings will feel it neverless.